I think that children (well girls really, let's be honest) need to be taught that masturbation is totally normal and everyone does it. Boys don't need this really do they, they are almost proud of their wanking!
I HAD to pop in here just to say, no, everyone does not do it. It's a cultural thing. As a teenager (I was born 1951) I had never heard of girls masturbating, never did it, never had the urge, never had the urge as an adult. I'm pretty sure none of my (female, teenage) friends did it either, as they would have said so -- we talked about everything, I knew when and with whom the lost their virginity etc. I thought only boys masturbated.
As I said, it's a cultural thing. If we are told it's what everyone does and it's fantastic, of course most people will get curious and try it. But you don't have to.
Basically I agree with this:
Secondly, I do not agree to any adult outside my home - essentially a stranger to me- opening up a dialogue about masturbation or sex or personal/intimate development with my child, especially when I am not present. It blurs the boundaries of appropriateness. I don’t care if they are a teacher, doctor, school counsellor, have a working with children check etc that all means nothing to me when it comes to the safety of my child.